Winter Wheat and Proso Millet Yield Reduction Due to Sunflower in Rotation

Abstract

Producers wishing to diversify crop production systems from the traditional winter wheat (Triticum aestivum L.)-fallow system of the central Great Plains need information regarding the impact of sunflower (Helianthus annuus L.) on subsequent winter wheat and proso millet (Panicum miliaceum L.) yields. This study was conducted to quantify winter wheat and proso millet yield reductions due to the lower available soil water that exists when sunflower is the prior crop in rotation. Eight crop rotations—including combinations of winter wheat (W), proso millet (M), corn (Zea mays L.) (C), sunflower (Sun), and fallow (F)—were established in 1990 and evaluated for yield, available soil water at planting, and crop water use in 1995, 1996, and 1997. The experiment was conducted at Akron, CO, on a Weld silt loam (fine, smectitic, mesic Aridic Paleustoll). Available soil water at wheat and millet planting was lower where sunflower had been the previous crop than where sunflower was not the previous crop. In dry years, rotations with sunflower as the previous crop had lower wheat and millet water use than other rotations, but averaged over 3 yr, there was no effect of sunflower on wheat or millet water use. Average wheat yield in a W-Sun-F rotation was about 30% lower than wheat yield from W-C-Sun-F, W-M-Sun-F, W-C-F, and W-F. Average millet yield in a M-Sun rotation was 43% lower than millet yield from M-W-C. Wheat yield declined by 178.5 lb/acre (3 bu/acre) for each inch decline in available soil water at planting. Millet yield declined by 295.6 lb/acre for each inch decline in available soil water at planting. In making the decision to include sunflower in crop rotations, producers will have to consider impact on subsequent crop yields, as well as costs of production, market value of crop, impact on pest problems, and total productivity of all crops in the rotation. Research Question Sunflower production offers central Great Plains producers an opportunity to diversify from the traditional winter wheat-fallow production system. But sunflower can leave the soil water profile in the top 72 in. very dry. The objective of this study was to determine the impact of sunflower on subsequent winter wheat or proso millet yields. Literature Summary Sunflower is adapted to the growing conditions of the central Great Plains and has an established market. But sunflower is a deep-rooted species capable of extracting large amounts of available water from deep in the soil profile. Yield of winter wheat and proso millet are linearly related to crop water use. Consequently, the low available soil water following sunflower production may reduce yield of subsequent wheat and millet crops. Study Description A crop rotation experiment was established near Akron, CO, in 1990. The following rotations were measured in 1995, 1996, and 1997 to quantify the effect of sunflower on subsequent winter wheat and proso millet yield: wheat-fallow (W-F), wheat-corn-fallow (W-C-F), wheat-sunflower-fallow (W-Sun-F), wheat-corn-sunflower-fallow (W-C-Sun-F), wheat-millet-sunflower-fallow (W-M-Sun-F), millet-corn (M-C), millet-sunflower (M-Sun), millet-wheat-corn (M-W-C). Soil water was measured at wheat and millet planting and harvest, and crop water use calculated by the water balance method. Wheat, millet, corn, and sunflower yields were taken at physiological maturity Applied Questions Does sunflower in rotation affect the amount of available soil water at wheat and millet planting? Available soil water at wheat planting averaged about 2.3 in. lower in the W-C-Sun-F and W-M-Sun-F rotations compared with the W-F and W-C-F rotations, and about 4.3 in. lower in the W-Sun-F rotation compared with the W-F and W-C-F rotations. Available soil water at millet planting averaged about 1.4 in. lower in the M-Sun rotation compared with the M-C and M-W-C rotations. Does the lower soil water at wheat and millet planting due to sunflower in rotation influence subsequent wheat and millet, yields? Wheat yield was reduced by about 179 lb/acre (3 bu/acre) for every in. less of available soil water at wheat planting (Fig. 1). Millet yield was reduced by about 296 lb/acre for every inch less of available soil water at millet planting. Average wheat yield in a W-Sun-F rotation was about 30% lower than wheat yield from W-C-Sun-F, W-M-Sun-F, W-C-F, and W-F (Fig. 2). Average millet yield in a M-Sun rotation was 43% lower than millet yield from M-W-C. Recommendations Producers should be aware that wheat yields in W-Sun-F rotations will almost always be lower than wheat yields in W-F production systems. On the other hand, when sunflower is only grown once every 4 yr (W-C-Sun-F, W-M-Sun-Full scientific article from which this summary was written begins on page 193 of this issue. F), wheat yields will probably only be reduced from the W-F yields when growing season precipitation is below normal. Additionally, including sunflower only once every 4 yr reduces pathogen and insect stresses on sunflower. Data from this study indicate that, on average, millet yields in a M-Sun rotation will be reduced about 43% from millet yields in a M-W-C rotation, but not greatly different from yields in a M-C rotation. In making decisions to include sunflower in crop rotations, producers should consider impact on subsequent crop yields, as well as costs of production, market value of crops, impact on pest problems, and total productivity of all of the crops in the rotation. Figure 1Open in figure viewerPowerPoint Relationship between available soil water and grain yield. Top: winter wheat yield and available water at wheat planting in 0 to 71 in. depth; bottom: proso millet yield and available water at millet planting in 0 to 35 in. depth. Figure 2Open in figure viewerPowerPoint Winter wheat and proso millet grain yield as affected by crop rotation at Akron, CO, averaged over 1995–1997 (P = probability of nonsignificant treatment differences, bars are LSD 0.10).